From a fellow grower: I purchased five Girl Scout Cookies Extreme Autoflower Seeds. All of them germinated, although much slower than other seeds. But only one of them sprouted, and it has only grown two inches, with a few small yellowish leaves, after 29 days. The strain is Girl Scout Cookies.
Over 3 weeks in vegetative stage.
Indoors in soil. Around 80°F and 45% humidity. Vivosun 200 watt grow light.
The soil is Happy Frog Soil. I use General Hydroponics nutrients as per the recommended mix ratio, at 50% dilution for seedlings. pH is around 6.0-6.5. I water seedlings sparingly with a small squirt bottle.
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First off, I wouldn’t be giving any nutes as of yet. Happy frog has plenty of nutrients in it for at least 4 weeks. I would suppose that it has nute lock.
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Yep like said above. I think they are burning up from the nutrients being added to new HF soil. Water with zero nutrients for about 4 weeks and use fresh soil for future sprouts.
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In HF soil definitely just ph’d water for the first 3-4 weeks until your ppm comes down to less than 1000. Also, seedlings only require a few mL of water a day. You could always put a dome on them until they touch the edges and then set them free. 
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From the color of the leaves looks like overwatering to me
How often are you watering and how much?
Feel the weight of the cup it should be very lite
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Definitely don’t feed. The cotyledons will feed the plant until they’ve established a root system, then the soil will carry it for a few weeks after that. The reason GH calls for feeding so early is because there are no nutrients growing hydroponically unless you add them.
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If the seedling in the picture is 3 weeks old and that color then it is lacking nutrients and possibly water. Your potting mix might be stuffed or the plant is too dry, especially if you aren’t watering it often and only using a spray bottle.
I like to sow the seed and then water the entire pot with a half strength liquid fertilizer. Then don’t water again until the top inch of soil is dry (stick your finger in the soil to see how dry it is).
A 3 week old seedling should be dark green and much bigger than that. It should have several sets of true leaves, not 1 set plus the cotyledons.
